Hyposalivation is represented by a reduced salivary flow rate and can be caused by etiologic factors such as systemic diseases and intake of various medications or by radiotherapy following head and neck cancer. The aim of this review was to compile data about the qualitative and quantitative changes of salivary components during hyposalivation, and to summarize their consequences for oral health. A Medline/PubMed/Scopus search was conducted to identify and summarize articles published in English and German that reported on etiology of hyposalivation and changes in the salivary composition due to hyposalivation of different origins. The search revealed 94 articles, 71 of which were original articles. Apart from the reduction of the salivary flow rate, the quality of saliva is strongly altered because of systemic diseases, medications, and radiotherapy, including increased viscosity and pH shift to more acidic values and changes in salivary protein compositions. Furthermore, hyposalivation may be accompanied by pronounced shifts in specific microbial components, in particular toward a highly acidogenic microflora. Moreover, therapy of hyposalivation is often restricted to palliative treatment (ie, saliva substitutes or gels). To prevent tooth tissue demineralization, clinicians should consider saliva substitutes that are supersaturated with calcium and phosphates and contain fluoride. Keywords: caries, drugs, hyposalivation, microflora, periodontitis, radiotherapy, saliva substitutes, Sjögren syndrome, xerostomia